Rotationally molded plastic containers for the storage and transportation of hazardous and non-hazardous liquid and free-flowing solid materials have many advantages over traditional steel storage containers. They are light-weight, corrosion-resistant, less expensive to produce, can be translucent for content level observation or made of colored plastic for color-coded content identification purposes and can be molded into a number of seamless custom configurations for storage, handling and transportation.
However, rotationally molded plastic containers also have inherent limitations. A primary limitation is that the plastic container is flexible, distorting under load pressure, and is subject to cracking, rupture, and puncture requiring additional non-plastic protection means external to the container.
Manufacturers have attempted to overcome these inherent limitations by constructing variations of square, rectangular, spherical, or cylindrically shaped containers. Each of these different shapes trades the above stated limitations. That is, it may reduce some limitation, but, in turn, introduces its own inherent limitations.
For example, square or rectangular shapes have single-walled sharp edges requiring additional protection from pressure cracking and handling damage. Further, the bulkhead walls bow and distort under content pressure requiring additional lateral support. The bowing also changes the dimensions, causing problems for pre-configured storage and shipping. Manufacturers have attempted to overcome these limitations by integrally molding vertical support ribs, and/or placing steel protective support cages around these types of square or rectangular containers.
Round and cylindrical type containers also have inherent limitations of bulging and distortion of the wall of the container requiring a steel support cage or steel retaining strap (hoop). In addition, round containers and cylindrical containers laid on their side(s) require additional support and handling means such as a saddle pallet and additional external means for stacking the same or like containers.
The addition of steel supporting structures and straping external to a plastic container vitiates the corrosion-resistant advantage of a plastic container. In addition, the external pallets have a tendency to move and twist free of the container when handled and transported.
As a result, manufacturers have resorted to a container-within-a-container concept with integrally attached pallet. For example, Bonar Plastics, Inc., of Ontario, Canada places a spherical plastic bottle container inside a square or cylindrical plastic support container with fitted cushions and integrally molded forklift tunnels. Plastic Products Manufacturing, Inc., of Fort Worth, Tex. makes a square plastic container inside a second protective square plastic container, and the two containers are thermally welded together to form a single integral unit which includes forklift access tunnels.
While the container-within-a-container concept helps to overcome some of the inherent limitations of the non-steel supported polyethylene container, they nearly double the cost of production over single containers, reduce the light-weight advantage of a single container, increase overall container assembly size or reduce capacity, and reduce or completely eliminate the content level observation feature of a translucent polyethylene container. In addition, the fully enclosed double container increases molding complexities resulting in the sacrifice or trade-off of integrally molded features such as for stacking of same or like containers, tie-down of the container during transportation, container top access to manways, and accessible recessed discharge valves.
Therefore, there is a need for a transportable, multi-use, non-corrosive, all polyolefin translucent plastic container and pallet system having a protected, strengthened, and cushioned single container with an integral, thermally attached pallet for handling and transportation, and having integrally molded features for stacking, tie-down, accessible manway, and near-100% draining of contents.